An Incomplete Systematic Review of Temporomandibular Disorders and Dental Occlusion Creates a Misleading Conclusion

Drs. Manfredini, Lombardo and Siciliani have again refused to consider the complete literature regarding the relationship between occlusion and the category of temporomandibular disorders (TMDs) within their systematic review. This is an incomplete systematic review including only studies of the visual bio-mechanical aspects of occlusion, while ignoring completely (using their own study exclusion criteria) the numerous, measured occlusal treatment studies involving the T-Scan technology, the synchronized BioPak EMG III module, and the Disclusion Time Reduction therapy (DTR) that have so often revealed repeatedly the neurologic etiology of occlusion for many TMDs. The fourteen excluded T-Scan studies span from 1991 all the way to 2016.^1–18 But this meta-analysis, like many that have preceded it, only includes papers where visual and biomechanical occlusal assessments were made as in Seligman and Pullinger.¹⁹ As such the “era” the authors are referring to is not ending; to the contrary, TMDs and their occlusal etiologies are here now as they always have been. These authors have simply refused to include the previous measured occlusion research publications from their systematic review.^1–14

This systematic review totally hides from the readers of the Journal of Oral Rehabilitation the T-Scan based DTR studies,^1–14 all of which clearly show the etiologic relationship of interfering occlusal contacts to specific TMDs. Was this omission intentional to defend the psychosocial theory of etiology? This incomplete systematic review is a prime example of how some authors can manage to eliminate valid science with their exclusion parameters, in this case the T-Scan based occlusion research studies.^1–18 This example should caution everyone from accepting at face value any future systematic review or meta-analysis conclusions, since what is left out, as in this example, could be more relevant than what is reviewed. The not included T-Scan studies clearly show that the neurology of the Pulp and Periodontal Ligament fibers²⁰ directly trigger the high muscle activities that are etiologic of the muscular TMDs symptoms.

The authors have apparently chosen to act as censors, withholding all of the T-Scan-based studies from the Journal of Oral Rehabilitation readership by cleverly excluding them and including only biomechanical studies that visually assessed patients and their stone casts. They reviewed studies of associations between numerous jaw relationships and the symptoms of TMDs. Although they actually did cite one T-Scan paper,²¹ they chose not to include it within their review. This systematic review would have been far more complete and more useful if the authors had included all of the published measured occlusion research.

A critical flaw within their overall approach to their review was their primary rationale that a lack of association equals a lack of causation. This is revealed in their question: “Is there any association between features of dental occlusion and temporo-mandibular disorders.” As every statistician knows, association does not equal causation. In the portion of the literature that they did review, each study that compared various jaw relationships to specific TMDs conditions did find at least one association. However, no amount of association proves (or disproves) an etiologic relationship. Thus, their entire review is defeated from the beginning. It was only in those reviewed studies where an association was sought between occlusal factors and “all TMDs” where no associations were found. The simple reason why can be understood by considering that the number of TMDs are at least 40 and that the likelihood of any one factor being associated with more than one or two of the 40 conditions is very low. The only way to scientifically establish an etiology is to defeat it consistently.

This is not the first publication by these authors to be called into question. Frey Adib,²² Dr. Roger Solow,²³ Dr. Barry Cooper²⁴ and Dr Ben Sutter et al²⁵ have all previously published reviews revealing inadequacies in their manuscripts. Without any limit to the irony, the lead author, who is known for writing 22 Systematic Reviews and Meta-Analyses on TMDs and bruxism in the past 10 years, recently published a paper criticizing the potential over-abundance of meta-analysis manuscripts.²⁶ They wrote in what turns out to be autobiographical, “The field of temporomandibular disorders (TMDs) and bruxism research has recently witnessed a publishing trend leaning towards an overuse of systematic reviews (SRs) that contribute little or nothing to current knowledge.”²⁶ While the premise is true, that review seems to be more anti-competitive than instructive.

There is another irony here that cannot escape our observance. These authors embrace the psychosocial theory of the etiology of all TMDs as promoted by the RDC/TMD followers and for which there is as yet no significant scientific support. Then they discard the best current scientific evidence for an occlusal etiology for at least some TMDs. This is clearly the definition of bias, favoring a psychosocial theory over a physiologic one by ignoring the physical evidence. Although strong correlations between somatic symptom disorders (SSD) and TMD have been revealed repeatedly, correlation does not equal causation. Thus, an etiologic relationship of SSD to TMDs has never been scientifically established. For example, no one has demonstrated any reliable psychosocial procedure that can successfully resolve TMDs, without which claiming etiology is pure speculation.

Worse, the theory that all TMD have a psychosocial etiology was recently succinctly disproven in a single study published in 2018, a T-Scan-based, Disclusion Time Reduction study.¹⁶ Not only were the physical symptoms relieved, but all of the significant and measured emotional disturbances were relieved as well after the purely physical treatments. While it is not safe to assume that DTR cures all SSD, when the somatic symptoms are secondary to occlusion, as they often are, correcting the occlusion can reliably eliminate them as well. It is safe, however, to conclude that many TMDs do have physical occlusal etiologies.

What is perhaps even more egregious is the editorial malfeasance in accepting and publishing an incomplete and biased systematic review. The responsibility to reject poor submissions cannot be left solely to the peer-reviewers. If all of their reviewers actually accepted this incomplete systematic review, the editor chose them poorly and is not providing adequate oversight to maintain journal quality. When a biased “systematic review” is published, not only is the readership misled, but TMD patients are also affected. The doctors who read a biased article in a scientific journal are misinformed, they pass the misinformation on to their patients and potentially forsake effective diagnostic or treatment procedures. The precision occlusal measurement provided by T-Scan/BioEMG III synchronization is impossible to obtain otherwise. The results of the many repeated T-Scan DTR treatment research studies must not be withheld from the dental profession. Practitioners must be allowed to decide for themselves what is appropriate treatment for their TMDs patients.

The biometric approach to diagnosis and treatment is changing the perception and perspective of dental medicine world-wide to improve patient care.²⁷ Professor Vardan Mkrttchian of HHH University, Australia, Editor-in-Chief of the International Journal of Applied Research in Bioinformatics (IJARB) wrote, “Digital technologies that complement the T-Scan System… …are aimed at the future of stomatology” and “…will be in demand among specialists who are looking forward rather than looking backward.”²⁸ The real era ending is the one limited to analog and unmeasured diagnostic and treatment procedures.

It must be acknowledged that four of the eighteen publications referenced here describing the successful T-Scan occlusal treatment studies were not available at the time these authors published their Systematic Review, but that is no excuse for ignoring all of the other fourteen. The last time we checked, studies that are not in the idealized randomized double-blind format still overwhelmingly trump completely non-existent studies to the contrary.

In response to some potentially valid criticisms regarding previous study formats, a randomized clinical occlusal trial in a single-blind format (due to the impossibility of blinding the treatment providers of the placebo occlusal adjustments) was recently published.¹⁸ This study, essentially a repetition of reference 16, reproduced the previous outcome of reducing or eliminating both the physical and the emotional symptoms of patients presenting with primary muscular TMD symptoms and concomitant emotional disturbances. The patients were randomly assigned to undergo either the immediate complete anterior guidance development coronoplasty (ICAGD) or a placebo occlusal procedure. It is our sincere hope that the next Systematic Review or Meta-analysis of the relationship between occlusion and TMD includes these significant studies.

An error does not become truth by reason of multiplied propagation, nor does truth become error because nobody sees it. - Mahatma Gandhi